EP 0 439 381 discloses a mechanism provided with such a restriction device, is which the relief consists of elastic lugs formed by a ring attached to the base of the duct, or even formed directly on the base of the duct. These lugs or tongues are disposed parallel to the axis of the duct and separate radially outwards to bear on the internal wall of the external duct at its base, or on a wall connected to this duct (possibly the decorative sheath which surrounds the external duct). This mechanism offers restriction which gives complete satisfaction. However, this excellent quality has a manufacturing cost which may be too high for mass production, less demanding in terms of quality.
It has been sought to produce restriction tongues directly in the wall of the cylindrical base to reduce manufacturing costs by virtue of a single injection molding operation. The restriction reliefs then consist of shoes or buttons disposed on a wall part, thinned or not, formed in the wall of the cylindrical base and cut (by molding) to form the tongue. That structure is shown, with various forms of tongues, for example, in U.S. Pat. Nos. 5,186,560, 5,186,561 and 5,324,126.
However, the quality of these mechanisms is low, especially for mass production.
It would therefore be advantageous to provide a restriction mechanism which achieves the same quality as that in EP 0 439 381, but is lower in cost.